After installing yum-priorities plugin yum takes forever to resolve
dependencies. With the plugin disables `yum list updates' takes about 7 seconds
on my Lenovo T60 with Centrino Duo & 2 gigs of RAM. With the plugin enabled
resolving dependencies took almost 1 hour (!). top showed that yum eats the CPU
all of the time.
And that was only 51 packages to update.

I found the same problem (it exists also with yum-protectbase).
I did some profiling and I found the problem is with yum itself. It is in the
_getSacks function of __init__.py in /usr/lib/python2.5/site-packages/yum
This gets called for each package that needs to be erased and when there are a
lot (like when using the dries repo at a lower priority than core/update which
means more than a 1000 deletes) it is a large slowdown.
The function checks for the existence of self._pkgSack but I guess the checks is
done by calling the __len__ which extracts the list of packages. I fixed the
problem by replacing
if self._pkgSack and thisrepo is None:
with
if self._pkgSack != None and thisrepo is None:
at the top of the _getSacks function.
With this change, using yum-priorities with the dries repo is not slow anymore.